It is often necessary to analyze materials to determine what substances they contain. This is true, for example, in the field of forensic science. Specifically, a forensic scientist may be called upon to analyze a sample from a fire or an explosion that occurred at domicile or place of business. In the case of a fire, the scientist may need to determine whether the fire was accidental or intentional (i.e., arson). In the case of an explosion, the scientist may need to identify explosive materials that were used to cause the explosion to assist law enforcement officials in identifying the individual or organization (e.g., terrorist group) responsible for the explosion.
In the case of fires, determinations as to the cause of the fires are typically made by analyzing fire debris, such as ashes, collected from various locations at the scene of the fire. The debris is placed in a container along with a carbon strip and the container is heated to cause the residue from any substances contained in the debris, such as gasoline or other ignitable liquids, to vaporize and then condense on the carbon strip. The carbon strip is then placed in a solvent to remove the substances and yield a mixture that can be analyzed using a gas chromatograph/mass spectrometer. As the various components from the mixture are output from the gas chromatograph, they are received by the mass spectrometer that breaks each component down and generates a mass spectrum of each component. A total ion chromatogram, which provides an indication of the total quantity, or intensity, of ions present for each component, can be created that comprises a graphic representation of the total ion intensity for each component in time as the components are chromatographically separated.
Once the total ion chromatogram is produced, it can be compared with the total ion chromatograms of various known ignitable liquids that could have been used to start the fire. Normally, such comparison is made by a forensics fire debris analyst familiar with ignitable liquids. Through the comparison, the analyst can draw a conclusion as to what ignitable liquid, if any, started the fire.
The above form of analysis has been used for many years and relies heavily on the expert, but subjective, opinion of the analyst. Furthermore, even when the total ion chromatogram from the sample is very similar to a total ion chromatogram of a suspected ignitable liquid, and it therefore appears likely that the analyst's opinion is correct, it is possible that the similarity could be diminished by the presence of residue formed from other materials which breakdown under the intense heat of a fire (e.g., carpeting, upholstery, foam padding, building materials) to produce substances in the debris that did not arise from the ignitable liquid. That possibility may undermine the conclusions made by the analyst and could result in an inability to prove that arson was in fact the cause of the fire. Moreover, the expert's conclusions are typically only considered valid if each total ion chromatogram used in the analysis was generated using the same equipment under the same conditions, thereby preventing the creation of a central database that could be universally referenced when making determinations as to the substances contained within a sample.